Adaptation of fibers in fast-twitch muscles of rats to spaceflight and hindlimb suspension

Abstract

The adaptation of single fibers in medial gastrocnemius (MG), a fast-twitch extensor, and tibialis anterior (TA), a fast-twitch flexor, was studied after 14 days of spaceflight (COSMOS 2044) or hindlimb suspension. Cross-sectional area (CSA) and succinate dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (GPD), and myofibrillar adenosinetriphosphatase (ATPase) activities were determined in fibers identified in frozen serial cross sections. Fibers were categorized as light, dark, or intermediate on the basis of myosin ATPase staining and alkaline preincubation and immunohistochemically as reacting with slow, fast, or both slow and fast myosin heavy chain monoclonal antibodies. Because there was a close relationship between these two means of categorizing fibers, all fibers were categorized on the basis of the immunohistochemical reaction. The percentage of slow- and fast-twitch fibers of the MG and TA were unchanged in either group. Mean fiber size of all fibers, irrespective of type, was unaffected in either muscle after flight or suspension. The fibers that expressed both fast and slow myosin heavy chains were smaller than control in the MG of both experimental groups. Compared with control, the SDH and total SDH activities in the MG were significantly less in suspended rats, with the fast-twitch fibers showing the largest difference. The ATPase activity in the MG was higher in flight than in control or suspended rats. There were no significant effects of flight on fibers of the TA. In contrast, the TA in suspended rats had higher GPD activities than either control or flight rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic Modulation of Muscle Fiber Properties Unrelated to Mechanical Stimuli

“…In a previous study [16], the soleus and the lateral gastrocnemius muscles from rats treated similarly were freeze-clamped with a pair of aluminum tongs cooled in liquid nitrogen, and the high-energy phosphate levels were measured biochemically [19,[27][28][29]. These results were compared with the data obtained by using 31 P-NMR in the present study, since the data from the in vivo 31 P-NMR analyses may represent values for the gastrocnemius and not necessarily for the soleus, which is located in the deep (close to the bone) region of calf. The responses of the phosphorus compounds to changes in creatine content were similar for both analyses [16]; thus, the non-invasive 31 P-NMR procedures were used in the present study.…”

“…Quantitative histochemical analyses of single fiber succinate dehydrogenase (SDH), ␣-glycerophosphate dehydrogenase (GPD), and myosin ATPase activities were determined as described previously [31,32]. The images of the same fibers analyzed for MHC expression were digitized as gray level pictures on a computer-enhanced image processing system (Nihon Avionics, Tokyo, Japan) and stored on magnetic optical disks.…”

Regulation of the Properties of Rat Hind Limb Muscles Following Gravitational Unloading.

“…Even though muscle fiber phenotype in slow-twitch soleus is shifted toward a fast-twitch type following spaceflight or hind limb suspension [3], such a transformation of fiber phenotype is not induced in fasttwitch plantarflexor [42] or dorsiflexor [43]. The specific activities of HAD decreased in both slow-(soleus) and fast-twitch muscles (plantaris and EDL).…”

Spaceflight results in increase of thick filament but not thin filament proteins in the paramyosin mutant of Caenorhabditis elegans

“…Absence of an antigravity muscle suggests that perception of microgravity effects may not occur in C. elegans. Microgravity effects on non-antigravity muscle are difficult to observe in vertebrates (Jiang et al, 1992;Caiozzo et al, 1996). However, the microgravity effect on the animals of unc-15 (e73) indicates that C. elegans does respond to gravity.…”